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1. MEMS-actuated metasurface Alvarez lens

   https://doi.org/10.1038/s41378-020-00190-6  

   Han, Zheyi; Colburn, Shane; Majumdar, Arka; Böhringer, Karl F. (October 2020, Microsystems & Nanoengineering)

   Abstract Miniature lenses with a tunable focus are essential components for many modern applications involving compact optical systems. While several tunable lenses have been reported with various tuning mechanisms, they often face challenges with respect to power consumption, tuning speed, fabrication cost, or production scalability. In this work, we have adapted the mechanism of an Alvarez lens – a varifocal composite lens in which lateral shifts of two optical elements with cubic phase surfaces give rise to a change in the optical power – to construct a miniature, microelectromechanical system (MEMS)-actuated metasurface Alvarez lens. Implementation based on an electrostatic MEMS generates fast and controllable actuation with low power consumption. The utilization of metasurfaces – ultrathin and subwavelength-patterned diffractive optics – as optical elements greatly reduces the device volume compared to systems using conventional freeform lenses. The entire MEMS Alvarez metalens is fully compatible with modern semiconductor fabrication technologies, granting it the potential to be mass-produced at a low unit cost. In the reported prototype operating at 1550 nm wavelength, a total uniaxial displacement of 6.3 µm was achieved in the Alvarez metalens with a direct-current (DC) voltage application up to 20 V, which modulated the focal position within a total tuning range of 68 µm, producing more than an order of magnitude change in the focal length and a 1460-diopter change in the optical power. The MEMS Alvarez metalens has a robust design that can potentially generate a much larger tuning range without substantially increasing the device volume or energy consumption, making it desirable for a wide range of imaging and display applications. 

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2. Characterization of Curved Piezoelectric Micromachined Ultrasound Transducers Fabricated by Chip-Scale Glass Blowing Technique

   https://doi.org/10.1109/LSENS.2023.3308112  

   Huang, Chichen; Khandare, Shubham P; Kothapalli, Sri-Rajasekhar; Tadigadapa, Srinivas (October 2023, IEEE Sensors Letters)

   Ultrasound has been extensively used and investigated in medical applications, such as medical imaging [1] and drug delivery [2], because of advantages such as noninvasiveness, good penetration, good sensitivity, and ease of use. Prior to the development of piezoelectric micromachined ultrasound transducers (pMUTs), conventional transducers were made of piezoelectric ceramics, such as lead zirconate titanate [3]. These materials when operated in thickness mode exhibit a large impedance mismatch between the transducer surface and medium resulting in lower bandwidth unless augmented with one or more matching layers. With the development of MEMS technology, improvements in MUTs have been realized in several aspects, such as wide bandwidth without the addition of matching layers [4], smaller cell size, therefore higher operating frequency and better resolution, and easier fabrication of large arrays at lower cost [5]. Despite lower electromechanical coupling coefficient, the low-power consumption feature makes pMUTs good candidates for a variety of applications, including intrabody communication [6] and fingerprint sensing [7]. 

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3. Solution‐Processed Disordered Plasmonic Surfaces as Optics for Infrared Imaging

   https://doi.org/10.1002/lpor.202400256  

   Mandal, Jyotirmoy; Brewer, John; Mandal, Sagar; Yang, Robert; Raman, Aaswath P (September 2024, Laser & Photonics Reviews)

   In recent years, thermal imaging and sensing technologies have seen dramatic increases in usage for a range of applications. However, the material cost and manufacturing complexity of infrared optics remain a major barrier toward their democratization. Here, a solution‐processed plasmonic reflective filter (PRF) is presented as a scalable, disordered, and low‐cost thermal infrared (TIR) optic. The PRF selectively absorbs sunlight and specularly reflects TIR wavelengths, with a performance comparable to state‐of‐the‐art infrared optics made of materials like Germanium. Unlike the latter, however, the PRF is fabricated using low‐cost materials and a “dip‐and‐dry” chemical synthesis technique, which enables orders of magnitude lower manufacturing costs. The PRF's optical functionality and integration into infrared imaging systems are experimentally demonstrated. The chemical synthesis technique also affords exceptional spectral tuneability and material compatibility compared to traditional fabrication methods. The PRF's tuneable and broadband TIR yield can be augmented by inexpensive dielectric or polymeric filters to yield novel capabilities such as wide‐area ambient temperature surveys. Practically, the PRF represents a significant advance toward democratizing the benefits of thermal imaging and sensing. Scientifically, it represents a previously unexplored optical functionality of disordered materials, and a new direction for versatile chemical synthesis in designing optical components. 

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4. Open loop control theory algorithms for high-speed 3D MEMS optical switches

   https://doi.org/10.1364/OE.367554  

   Pollock, C.; Pardo, F.; Imboden, M.; Bishop, D_J (January 2020, Optics Express)

   There is a world-wide push to create the next-generation all-optical transmission and switching technologies for exascale data centers. In this paper we focus on the switching fabrics. Many different types of 2D architectures are being explored including MEMS/waveguides and semiconductor optical amplifiers. However, these tend to suffer from high, path-dependent losses and crosstalk issues. The technologies with the best optical properties demonstrated to date in large fabrics (>100 ports) are 3D MEMS beam steering approaches. These have low average insertion losses and, equally important, a narrow loss distribution. However, 3D MEMS fabrics are generally dismissed from serious consideration for this application because of their slow switching speeds (∼few milliseconds) and high costs ($100/port). In this paper we show how novel feedforward open loop controls can solve both problems by improving MEMS switching speeds by two orders of magnitude and costs by a factor of three. With these improvements in hand, we believe 3D MEMS fabrics can become the technology of choice for data centers. 

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5. Metalens-Based Miniaturized Optical Systems

   https://doi.org/10.3390/mi10050310  

   Li, Bo; Piyawattanametha, Wibool; Qiu, Zhen (May 2019, Micromachines)

   Metasurfaces have been studied and widely applied to optical systems. A metasurface-based flat lens (metalens) holds promise in wave-front engineering for multiple applications. The metalens has become a breakthrough technology for miniaturized optical system development, due to its outstanding characteristics, such as ultrathinness and cost-effectiveness. Compared to conventional macro- or meso-scale optics manufacturing methods, the micro-machining process for metalenses is relatively straightforward and more suitable for mass production. Due to their remarkable abilities and superior optical performance, metalenses in refractive or diffractive mode could potentially replace traditional optics. In this review, we give a brief overview of the most recent studies on metalenses and their applications with a specific focus on miniaturized optical imaging and sensing systems. We discuss approaches for overcoming technical challenges in the bio-optics field, including a large field of view (FOV), chromatic aberration, and high-resolution imaging. 

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